Poster abstract details

Water fountain stars represent a transitional stage between the AGB and planetary nebulae, when the mass loss changes from spherical to bipolar. This group is characterized by water maser emission at 22 GHz spread over more than 100 km\,s$^{-1}$ (even 500 km\,s$^{-1}$ at the most extreme case), and a clear bipolar morphology. The objective of this work is to detect and further study the circumstellar envelope where the bipolar outflows are currently emerging. We have used the 30m IRAM radio telescope at Pico Veleta to search for CO and $^{13}$CO $J=1\rightarrow 0 and 2\rightarrow 1$ line emission associated to all the water fountain stars visible from the telescope. We have detected CO and $^{13}$CO emission in eight sources over a total of ten. Most of this emission, however, come from foreground/background galactic clouds. Just in two cases we detect clear signposts of emission arising from the circumstellar envelopes; a third case is considered as tentative. Using the observational line parameters we have modeled the line emission in the two positive detections, and for the first time some global physical parameters of the circumstellar envelope corresponding to a water fountain star were provided. These results encourage new searches using more sensitive observations and higher angular resolutions. Another natural follow up to these results is also to start a study of other chemical compounds, as well as the search for other, undiscovered water fountain stars.